Process for providing high density dry spun



March 10, 1964 M DAVls ETAL 3,124,631

PROCESS FOR PliOVIDING HIGH DENSITY DRY SPUN ACRYLONITRILE POLYMER FILAMENTS Filed March 22. 1961 INVENTORS MERTON LOUIS DAVIS |..ou|s CHARLES PALMER ATTORNEY United States Patent PROCESS FOR PROVIDING HIGH DENSITY DRY SPUN ACBYLONITRILE POLYMER FILAMENTS Merton Louis Davis, Camden, S.C., and Louis Charles Palmer, Dordrecht, Netherlands, assignors to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed Mar. 22, 1961, Ser. No. 97,524 4 Claims. (Cl. 264-290) This invention relates to a process for preparing high density acrylonitrile polymer filaments. More particularly, the invention relates to an improved process wherein acrylonitrile polymer filaments are concurrently washed and drawn in a cascading water bath.

Dry-spun acrylonitrile polymer filaments generally issue from the spinning cell in a solvent-laden condition, i.e., containing from about 15% to 40% solvent. In order to provide suitable textile yarns, it is necessary to substantially reduce the solvent content, e.g., to approximately 5% or less, and to draw the filaments to improve their physical properties. Washing and drawing of such filaments by prior art processes has generally required the use of carefully regulated chemical baths and/ or complicated procedures. Attempts to simplify such procedures have produced low density filaments containing numerous microscopic voids which are believed to cause, at least in part, poor finish retention and an excessive amount of fly in the fabrication of yarn. In general, the filaments produced are also limp and soggy.

It is, therefore, an object of this invention to provide a novel wash-draw process for preparing high density acrylonitrile polymer filaments. Another object of this inven tion is to provide a readily controllable process whereby high density filaments which exhibit a high residual shrinkage are produced. A further object of this invention is to provide a process for preparing acrylonitrile polymer filaments which exhibit good processability and a desirable crisp and lively hand in finished textile articles.

The objects of this invention are accomplished by a process in which a solvent-laden, continuous filament bundle is concurrently washed and drawn a predetermined amount in a plurality of reservoirs of a cascading water bath. For convenience in describing the bath, the reservoirs are referred to as comprising a lower and upper flight of the cascade bath. In the novel process, the filament bundle is passed at a predetermined rate into at least one lower reservoir of the bath which is heated to a temperature from about 90 to 100 C. The filaments are successively passed into and withdrawn from the remaining lower reservoirs at a controlled rate of speed to provide from about 40% to about 70% of the total draw to be imparted. From the lower reservoirs, the filaments are passed to the upper reservoirs which are heated to a temperature from about 50 to 88 C. The rate of travel through the upper reservoirs is adjusted to impart the remainder of the desired draw. As the filaments leave the uppermost reservoir, water, which is heated to a temperature from 50 to 60 C., is impinged onto the filaments or, alternatively, the filaments are immersed in an aqueous bath which is heated to a temperature within the recited range. The water is directed to the uppermost reservoir to provide the cascading flow through the bath. By controlling the rate of travel through the bath and the number of reservoirs, the solvent content of the filaments is reduced to the desired level, preferably 5% or less, and the filaments are drawn from about 2 to or more and preferably 2 to 8 times their original length.

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For further explanation of the process, attention is invited to the figure of the drawing which is a diagrammatic representation of the apparatus suitable for carrying out the process of this invention.

In the figure, a bundle of acrylonitrile polymer filaments 1 is fed from a supply source between squeeze rolls 2, 3 and 4 into the lowermost reservoir 5 of a cascading water bath. The bundle 1 is fed under roll 6 and withdraw from reservoir 5. Bundle 1 is then fed alternately over and under rolls 7, 8, 10, 11, 13, 14, 16, 17, 19, 20, 22, and 23 as it is successively passed through ascending reservoirs 9, 12, 15, 18, 21, and 24. After bundle 1 leaves reservoir 24, it is fed between a second set of squeeze rolls 25, 26, and 27, at which point water is sprayed onto the bundle from nozzle 28. The water not retained on the filament falls onto the sloping portion 29 of housing 30 and is directed into reservoir 24. The water cascades from the uppermost reservoir 24 to the lowermost reservoir 5. Wash liquor is constantly removed from reservoir 5 through outlet 38 to provide a predetermined level in the lowermost reservoir. Each of the reservoirs is heated by steam coils 31 to 37, inclusive.

In general, the number of reservoirs comprising the cascading bath may vary over a wide range, depending on the amount of solvent which must be removed from the filaments. For example, if the solvent content is relatively low, as few as three lower reservoirs and two upper reservoirs may be utilized. If the solvent content is higher, seven to twelve reservoirs may be required. Generally, nine or ten reservoirs are suitable. Preferably, a greater number of reservoirs are included in the lower flight of the bath.

- While the number of reservoirs may vary, it is essential that the lower reservoirs be maintained at a temperature in the range from to 100 C., and preferably to C., and that the upper reservoirs be maintained at a temperature from 50 to 88 C. It is preferred that the temperature profile approach the upper limit for the temperature in the lowermost reservoir and progressively decrease to a point near the lower limit in the lower flight. Likewise, a decreasing temperature profile is preferred in the upper flight toward the point of exit of the filaments.

The drawing of the filaments may be accomplished in any one of the reservoirs within the respective flights. It is essential, however, to accomplish from 40% to 70% of the drawing as the filaments pass through the reservoirs of the lower flight, with the remainder of the drawing being performed as the yarn traverses the upper flight.

The following example, in which parts and percentages are by weight unless otherwise indicated, further illustrates the present invention.

' EXAMPLE Acrylonitrile polymer filaments were prepared by dry spinning a dimethylformamide solution of a terpolymer containing about 93.5% acrylonitrile, 6.0% methyl acrylate, and 0.5% sodium styrene sulfonate. The filaments, which contained 25% of the solvent, were collected in the form of ropes which had a total denier of about 185,000 (20,550 tex) with individual filaments having an as-spun denier of about 10 (1.1 tex). The several ropes collected were fed at a speed of 65 yards per minute to a wash-draw apparatus of the type shown in the figure, with particular individual ropes being fed through the apparatus in side-by-side relationship.

In the apparatus utilized, the cascading bath was comprised of nine separate reservoirs, with certain of the upper rolls geared to draw the rope at four stages along Reservoir No. Tempegature, Draw Ratio 4. 52X Total As the ropes passed through the exit squeeze rolls, fresh extraction water at a temperature of 50 C. was sprayed onto them at a rate of about 2600 pounds per hour. The washed and drawn filaments contained 2% solvent.

The ropes were then passed through a steam chamber to raise their temperature to about 70 C. They were then passed through a conventional stuffer box crimper to which steam was supplied at a pressure of 2 pounds per square inch gage. The hinged outlet clapper was maintained at about 60 pounds per square inch gage. The crimped ropes were subsequently cut to staple length, dried, and opened. The staple fiber had a residual shrinkage of about 17% and a density of 1.183. The yarn exhibited a crisp, lively hand and excellent anti-static properties.

While the process of this invention has been illustrated with filaments prepared from an acrylonitrile terpolymer, filaments of acrylonitrile homopolymers and copolymers containing at least 85% polymerized acrylonitrile may be treated by the process, e.g., acrylonitrile polymers containing up to 15% of copolymerizable ethylenically unsaturated monomers such as those described in U.S. Patents 2,436,926 and 2,743,994, as'well as those containing a small amount, e.g., up to about of a sulfurcontaining monomer of the type described in U.S. Patents 2,527,300, 2,837,500 and 2,837,501. In addition, mixed polymers wherein one of the polymers of the mixture contains at least 85% acrylonitrile may be utilized to prepare filaments which are treated by the present process. The polymers from which the filaments are prepared should preferably have an average molecular weight in the range from about 40,000 to 150,000.

In defining the process of this invention, it is to be understood that the term cascading water bath is not to be restricted solely to water as the wash liquor. Suitable adjuvants such as fugitive dyes, extraction aids, and the like, may be incorporated in the wash liquor. These adjuvants may be sprayed onto the filaments as they leave the final reservoir or they may be separately added to one or more of the reservoirs.

The filaments treated by the process of this invention may be subjected to various after-treatments to enhance certain properties. For instance, staple fibers prepared from about90 to 100 as described in the foregoing example, when treated in a stufling box crimper without a preliminary steaming treatment and without steam being supplied to the stuffer box and with the outlet clapper maintained at 55 pounds per square inch gage, exhibit substantially the same physical properties as the staple fibers of the example but have somewhat reduced crimp frequency and amplitude. Such fibers also have a higher residual shrinkage, e.g., in the range from about 20-24% after cutting and drying.

The filaments of this invention exhibit a high density. In addition, they exhibit enhanced processability, especially on cotton system spinning equipment even after they have been in storage for extended periods of time, e.g., as long as six months, The fibers produced also display substantially improved mass cohesion and reduction in fly during processing. These fibers may be utilized alone or in blends-with other synthetic and natural fibers in numerous textile applications.

As many widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that this invention is not to be limited to the specific embodiments thereof except as defined in the appended claims.

We claim:

1. In a process for providing high density, dry-spun acrylonitrile polymer filaments wherein said filaments are concurrently washed and drawn at least two times their original length by successively passing a bundle of undrawn, solvent-laden filaments into a plurality of reservoirs of a cascading water bath, the steps comprising heating the lower reservoirs of said bath to a temperature C, successively passing said filaments into the first and each succeeding lower reservoir and withdrawing them at a rate to impart from about 40% to about of the total draw, heating said upper reservoirs to a temperature from about 50 to 88 C., and successively passing said. filaments into and withdrawing said filaments from each of said upper reservoirs at an increased rate to impart the remainder of said draw, and thereafter directing water at a temperature from about 50 to 60 C. onto said filaments and into the uppermost reservoir to provide cascading flow through said bath.

2. The process of claim 1 wherein the temperature profile of said cascading water bath progressively decreases from said first lower reservoir to the last upper reservoir.

3. The process of claim 1 wherein said lower reservoirs are heated to a temperature from to C.

4. The process of claim 3 wherein said filaments are drawn a total amount of from about two to eight times their original length.

References Cited in the file of this patent UNITED STATES PATENTS 2,611,929 Hoxie Sept. 30, 1952 2,723,900 Hooper Nov. 15, 1955 FOREIGN PATENTS 546,552 Canada Sept. 24, 1957 

1. IN A PROCESS FOR PROVIDING HIGH DENSITY, DRY-SPUN ACRYLONITRILE POLYMER FILAMENTS WHEREIN SAID FILAMENTS ARE CONCURRENTLY WASHED AND DRAWN AT LEAST TWO TIMES THEIR ORIGINAL LENGTH BY SUCCESSIVELY PASSING A BUNDLE OF UNDRAWN, SOLVENT-LADEN FILAMENTS INTO A PLURALITY OF RESERVOIRS OF A CASCADING WATER BATH, THE STEPS COMPRISING HEATING THE LOWER RESERVOIRS OF SAID BATH TO A TEMPERATURE FROM ABOUT 90* TO 100*C., SUCCESSIVELY PASSING SAID FILAMENTS INTO THE FIRST AND EACH SUCCEEDING LOWER RESERVOIR AND WITHDRAWING THEM AT A RATE TO IMPART FROM ABOUT 40% TO ABOUT 70% OF THE TOTAL DRAW, HEATING SAID UPPER RESERVOIRS TO A TEMPERATURE FROM ABOUT 50* TO 88*C., 